I say go for Tidal Wave Grimoire (it's what I use). It's Levi's drop and you need to get a mirror. Levi Ex can be cleared with DF party more so than T5. The mirror drops sucks, though. I went three weeks without seeing a mirror, but then do a farm party and we get three mirrors in five runs. Ramuh is pain, and is currently my wall. I think Levi is the way to go - it's more accessible than the Allagan book and Ramuh's book. The Wave Grimoire (sans mirror) is still a decent book.